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Homework Help: Venturi Metter - Conceptual Question

  1. Feb 4, 2009 #1
    I am working on a lab, and *think* I understand what is going on, but looking for a double check of my logic from someone more experience than I am.

    In short its a multi-piezometric tube venturi meter, with 1 throat near the begining, a couple of expansions, and a control valve near the end. We took measurements at the various tubes, and I am trying to summarize the data qualitatively.

    The 9 piezometric tubes on the pipe are setup as follows: (points A - H)

    A) 26mm diameter pipe (13mm in front of the constriction, 25mm long)
    B) 16mm throat (16 mm long as well)
    C) 26mm pipe that comes after a gradually increasing pipe diameter
    D) 51mm pipe that comes after a sharper increasing pipe diameter (totall diffuser = 89mm)
    E) A control valve in the 55mm pipe
    F) A straight 51 mm pipe section
    G) A continued straight 51 mm pipe
    H) The end of the meter (still 51 mm diameter pipe, total pipe lenght = 130 mm)

    Here is my understanding is regarding the data we took
    (sorry about the formatting, but hopefully you can understand my notes):

    (flows) Q (l/s) A(mm) B(mm) C(mm) D(mm) E(mm) F(mm) G(mm) H(mm) I(mm)
    flow 1 .18 370mm 332mm 360mm 356mm 360mm 318mm 324mm 322mm 222mm
    flow 2 .24 330mm 274mm 320mm 316mm 324mm 254mm 262mm 260mm 160mm
    flow 3 .28 370mm 284mm 350mm 346mm 354mm 260mm 272mm 270mm 168mm

    Here is what I think happens as water flows through the meter.....

    'A' p builds due to upcoming constriction
    'B' v increases, p drops as water is 'sucked' along
    'C' p returns to almost state 'A' (losses occur)
    'D' slight drop in p as area increases slightly
    'E' p builds in front of valve obstruction
    'F' p drops a little after passing valve
    'G' p continues to drop as near opening
    'H' p still dropping
    'I' at end, p as close to 0 as possible (within this system).

    Am I on the right track?

  2. jcsd
  3. Feb 5, 2009 #2
    Sounds pretty reasonable.

    I am not any sort of expert in this matter, but did you try to compare the average pressures you found to the radius, cross-sectional area, or volume of the various pipe-sections to detect any relationship?
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